Tool tongs of this kind are known. They are known either individually or in the form of tool changers in machining tools or machining lines. Here, machining tools of a machine tool supplied in a tool supply are transported into the machining spindle or removed from it. These processes are executed completely automatically, that is without manual interaction of a worker. It is known in the state of the art to form tool tongs of this kind from a basic element and a tongs clamping element. These two basic elements of the tool tongs are manufactured from cast material. The basic element is, for example, somewhat more massive than the tool clamping element. This is arranged, for example, moving or swiveling via an axis at the basic element, and preferably mounted on springs. It is possible here to open the tongs by pressing against the spring force. When the force is released, the tongs clamping element is pushed against the tool and its appropriate holding elements or clamping elements, and thus clamped. When the tool is clamped in the tongs, the tongs can be moved away from the spindle by suitable drives, and then, for example, be swiveled to a tool magazine. It is also possible to remove a tool from a tool magazine, and to transport it to the spindle of the machine tool. The tongs are opened again there when, for example, the tool is positioned in the magazine or in the spindle. Of course, also a tool changer supplying a multitude of machining tools for very different machining processes or operations can be provided instead of the tool magazine. Manufacturing the tool tongs is very complicated in the state of the art as these are cast elements. The casting molds have to be supplied accordingly, casting comes with high energy consumption, and it requires also a lot of time. Furthermore, subsequently, after casting, the tongs elements, that is basic element and tongs clamping element, have to be machined mechanically so that the corresponding holding and clamping elements are configured exactly correspondingly to the clamping elements of the tools. The large weight of the tool tongs resulting from the way of manufacturing is another disadvantage of the tool tongs of the state of the art.
In the specification DE 35 31 160 a pair of tool tongs designed as described before has become known. The tool tongs are here configured in two pieces, a tongs clamping element being arranged seesaw-like mounted on springs on a basic element.
Besides the already described disadvantages of the state of the art with a spring-mounted seesaw, of course, in embodiments of this type the problem arises that the spring can fatigue fast because of the permanent heavy load and break. Of course, this requires an earlier exchange of the entire tool tongs in the machine tool, resulting in corresponding expenses. The lifetime of these tool tongs are accordingly way too short. Even in the next solution of the state of the art, described farther above, a swiveling system is shown acting spring-loaded. The swiveling axis extends here parallel to the tool axis, and, when appropriate force is applied on the tool, the tool will be drawn out of the tool tongs in a movement orthogonal to the tool axis. In this case, the spring-mounted swiveling lever yields. A spring-mounted swiveling lever has, of course, the same disadvantages as the already before discussed embodiment, as a spring has the disadvantage that its spring force decreases when loaded permanently, and/or the spring becomes brittle and thus breaks easily. Of course, the discussed tool tongs are inserted in machine tools where tool changes have to be carried out rather frequently so that this spring is, of course, loaded considerably. Besides, the linear drive is, so to say, provided at the tongs basic element, and moves only one tongs part or one tongs half for opening and closing the tool tongs. The rest of the tool change process is carried out via a swiveling axis so that the tool, when moved in or out, still exerts a suitable force on the tool tongs half in order to maintain this swiveling movement. The result is a corresponding wear at the tool and the tongs. Furthermore, it cannot be guaranteed that the tool tongs can be operated altogether actively, that means that in the tool change position even another force has to act on the tool to move it out of the tongs. Additionally, the shifting operation of the linear motor is rather time-consuming so that it has been decided to provide another tongs part with an axis so that it can swivel elastically. In contrast to the solution according to the invention, here also the swiveling axis for the swiveling tongs part is arranged exactly in the direction of the longitudinal axis of the tool, what is a disadvantage altogether, as a larger force is required for effecting the opening and closing operation. The solution according to the invention completely removes these problems.
Additionally, it has to be stated that a spring as used in the state of the art shows basic disadvantages. It can slacken or break, and thus not execute correctly the holding function. As an additional component, a spring is very complicated to assemble. Furthermore, also break and wear can obstruct essentially the reliability of the tool tongs or the gripping or holding operation.
A tool changing device is known from the specification DE 20 2010 003 378. This tool changing device has at least one gripping device containing a first gripping element and a second gripping element that can move between a clamping position and a changing position for the releasable holding of a tool holder or a tool. A part of the movable second gripping element is designed as rotor of an electric linear drive.
A gripper for articles is known from the specification EP 355 271. Here, an elastic tongs element is provided in the carrier part, the elasticity being accomplished by appropriate recesses in the tongs material. When the tool moves in or out, here a certain inherent elasticity through the spring-like design of the tool tongs in the shape of the recesses in the tongs is used for bending up the tongs half and then to move back again by the inherent elasticity. The effect is here that only by the motion force of the tool, when it is pushed in the tool tongs, the tongs open or close, when the tool is positioned at the correct point. In truth, in this solution, also a high wear of the tool or the corresponding tool holder and the tool tongs has to be taken into account.